Automated train control systems are being utilized with increased frequency in the U.S. and in other countries around the world, both for freight and for passenger rail systems. In the U.S., recent legislation requires the installation of a positive train control (PTC) system on Class 1 freight rail lines and all tracks carrying passenger trains by 2016. Automated train control systems can come in many varieties. For example, the assignee of the present application currently offers a system sold under the TRAIN SENTINEL® mark as described in several U.S. patents, including U.S. Pat. Nos. 6,996,461, 6,865,454, and 6,845,953 (each of which is hereby incorporated herein by reference). Another PTC system is sold by WABTEC under the ETMS® mark. Systems such as these utilize vehicle borne computers that determine train position using global positioning system (GPS) receivers, wheel tachometers and other devices, and enforce movement authorities received from a central office by activating the train's brakes via a brake interface to prevent the movement authorities from being violated. Such systems often include onboard databases with locations of grade crossings, switches and other configurable devices and interrogate such devices to ensure correct configuration prior to the train's arrival. Still other PTC systems include the ITCS™ and ACSES™ systems, which utilize track mounted transponders or wayside beacons and transmit authorities, grade crossing and switch data from the wayside to computers on board the trains.
In PTC systems, having the correct train length is critical to ensuring that the end of a train has cleared a position such as a block boundary or a switch point. U.S. Pat. No. 6,081,769 uses GPS receivers in an end of train unit and at the head of train to determine train length. This technique is less than optimal because of position errors that are possible with GPS receivers and due to differences in train length that can result from slack between cars (which can be as much as one foot), which can be significant for freight trains that often exceed 100 cars in length. In the aforementioned TRAIN SENTINEL® system, the train operator enters the train length as given to him by the dispatcher on a pendant. This leads to a potential human error, both in the form of a miscommunication or improper entry of the information, or because the information is incorrect due to an error by classification yard personnel responsible for forming the train/consist.
Having the correct train weight is also important in a PTC system because the train weight, and sometimes the positions of the cars in the consist, are used in the calculation of the braking curve. There is a safety factor built into the braking curve, but it is still better to have the most accurate weight possible. If the train is lighter than the amount used by the PTC system for the braking curve calculations, the braking curve will force brake activation earlier than is necessary, causing less efficient operation. If the train is heavier than the amount used by the PTC system for the braking curve calculations, the safety margin is eroded and possibly exceeded, leading to a potentially unsafe condition.
AEI (automatic equipment identification) tags, which are a form of RFID tag, and AEM (automatic equipment maintenance) tags are currently used by railroads to track the movement of railroad cars and freight onboard those cars (hereinafter, AEI will be used to refer to both AEI and AEM tags). The American Association of Railroads (“AAR”) has mandated the use of these tags, and it is estimated that in excess of 95% of the North American railroad car fleet has been outfitted with AEI tags. AEI tags are typically mounted on both sides of a railroad car approximately 40 inches above grade level and are read by special readers using radio frequency signals. Existing readers are typically located outside of the yard at various places along the wayside. There are believed to be more than 3,000 AEI readers installed in North America. To the knowledge of the inventors, the information from AEI tag readers has not been used for train control purposes such as to detect and/or correct errors in data used by the train and or in constructing consists.